An X-ray computed tomography (CT) apparatus is a device that images the inside of a subject by scanning the subject by using X-rays and performing processing on collected data with a computer.
For example, the X-ray CT apparatus exposes the subject to X-rays a plurality of times in different directions and detects signals of X-rays that transmitted through the subject with X-ray detection elements (hereinafter, simply described as “detection elements”). The detection elements include scintillators and a photodiode (PD) chip, for example. The X-ray CT apparatus collects the detected signals, and performs A/D conversion and then preprocessing and others on the collected signals to generate projection data. The X-ray CT apparatus then performs reconstruction processing based on the projection data and generates an image.
In the X-ray CT apparatus, an output line may be provided for each detection element and a simultaneous collection method in which the signals detected by the respective detection elements are simultaneously collected may be employed. In this case, as a method to take out the signals from the respective detection elements, available are a method using bonding wire and a method using a ball grid array (BGA).
In the method using bonding wire, the signals are collected by extending signal lines up to the end of the PD chip. That is, in this method, because the signal lines run through between the detection elements, the light-receiving areas of the detection elements are impaired. In contrast, in the method using a BGA, because the signals are collected from respective electrodes on the bottom of the PD chip with electrodes in a ball shape such as solder balls, the light-receiving areas are not impaired. Thus, in a multi-line X-ray detector, the method using a BGA is widely employed.
Meanwhile, in the X-ray CT apparatus, to enhance a spatial resolution, achieving high definition of detection elements has been advancing. When the above-described method using a BGA is employed, the pitch (width) of the ball-shaped electrodes narrows along with the implementation of high definition. However, there are limitations on the pitch of the ball-shaped electrodes formed between the PD chip and a substrate that is for collecting the signals from the PD chip. Thus, achieving high definition by the method using a BGA depends on the pitch of the ball-shaped electrodes.